CVD (Chemical Vapor Deposition) preparation method of multi-layer reduction boat

Abstract

Aiming at the defects in the prior art, the invention provides a CVD (Chemical Vapor Deposition) preparation method of a multi-layer reduction boat, and the problem that a nickel-chromium reduction boat is easy to deform is solved by taking an inorganic non-metal material as a base material; and the boron carbide surface layer is constructed by utilizing the characteristics of low surface energy and difficult adhesion of boron nitride, so that the problem of easy powder adhesion is solved. Meanwhile, nickel-tungsten alloy is electrically deposited on the two layers of materials, so that the internal binding force of the coating is maintained, and the coating is prevented from cracking and falling off. Metal nickel is added into tungsten, so that the internal binding force of the coating can be effectively maintained, and meanwhile, a large number of experiments prove that a boat of the nickel-tungsten alloy is normal and does not deform within 24 hours at the temperature of 1350 DEG C. And due to the use of metal nickel, the material cost is greatly reduced, and the internal binding force of the coating is increased. In conclusion, according to the reduction boat, the transition gradient layer is firstly formed on the body, then the boron nitride coating is formed on the transition gradient layer, the anti-sticking and anti-diffusion effects can be achieved, the production cost is reduced, and the reduction boat is stable in performance and long in service life.

Description

Technical Field

[0001] The present application relates to a CVD preparation method for a multilayer reduction boat, belonging to the field of high temperature materials and their preparation. Background Art

[0002] At present, the main method for industrial production of tungsten carbide powder is to reduce tungsten oxide in a hydrogen atmosphere. In the process of reducing tungsten oxide in a high-temperature hydrogen atmosphere, the tungsten oxide needs to be placed in a special reduction boat container. One of the keys to tungsten powder quality control lies in the reduction process of tungsten oxide, so the reduction boat cannot bring external impurities into the tungsten powder. In addition, the use scenario of the reduction boat is generally a reducing atmosphere such as hydrogen and a high temperature not exceeding 1300°C. In addition, in the process of hydrogen reducing oxides, a small amount of water vapor, NH3 and other gases may be produced during the reaction. These gases will corrode specific materials (such as graphite, some metals and carbides) at high temperatures.

[0003] The reduction boats widely used in the current industry are mainly alloy boats, mainly including stainless steel reduction boats and Ni-Cr reduction boats. Compared with Ni-Cr boats, stainless steel boats have relatively low high temperature strength, are suitable for relatively low temperatures, and are more easily deformed. Therefore, nickel-chromium alloy reduction boats are commonly used in the production process of metal tungsten powder. Although compared with the first generation of reduction boats (mainly graphite boats), nickel-chromium alloy boats have been improved in corrosion resistance and service life. However, these boats usually have the following disadvantages: sticking to the boat makes it difficult to unload the boat and wastes materials, and a heavy hammer is required to unload the material; the alloy density is large, resulting in large furnace tube load-bearing and boat pushing resistance; the alloy boat will deform during long-term use and cannot be used, and the sticking problem of the alloy boat makes it difficult to automate the production line. Therefore, it is urgent to design and develop a new type of anti-sticking boat, anti-deformation, anti-cracking, and anti-element diffusion coating reduction boat. Due to the widespread use of nickel-chromium alloy boats in the industry, the development of a new generation of reduction boats has become a very important research in the tungsten powder reduction industry.

[0004] In recent years, Hunan Carbon Peak Materials Technology Co., Ltd. has announced two patents with application numbers 202211433398.9 and 202310800632.5. Among them, the patent with application number 202310800632.5 adopts a splicing process, the lining is made of ceramics such as alumina, silicon nitride or silicon carbide, and the outer shell is made of high-strength and corrosion-resistant metal materials. This process can increase the durability and stability of the boat to a certain extent. However, in the process of repeated heating and cooling, this process inevitably has problems such as insufficient durability and short service life. The patent with application number 202211433398.9 uses chemical vapor deposition to deposit pyrolytic carbon on the surface of the graphite preform. The matrix material is graphite and the outer layer material is pyrolytic carbon. This process can improve the surface strength, density and chemical stability of the material to a certain extent. However, with this deposition process, it is not easy for the newly deposited carbon material to form a strong covalent bond on the surface of the original carbon material, and there are still problems such as weak bonding between carbon materials, insufficient durability, and short service life. Based on the prior art, this application adopts a two-step process. First, a metal layer of nickel-tungsten alloy is plated on the silicon carbide material using electroplating technology, and then a boron nitride non-stick layer is deposited on the outside of the metal layer using CVD technology. The process adopted in this application utilizes the better bonding force of the metal layer to improve the problems of poor durability of the boat and weak bonding force of the layers of the boat brought about by the prior art to a certain extent. At the same time, the non-stick performance of the reduction boat is improved. To a certain extent, the problem of the short service life of the reduction boat is solved. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present application is a new type of reduction boat that uses inorganic non-metallic materials as the base material to solve the problem of easy deformation of the nickel-chromium reduction boat; the low surface energy and non-stick characteristics of boron nitride are used to construct a boron carbide surface layer to solve the problem of easy powder adhesion. At the same time, nickel-tungsten alloy is electroplated on the two layers of material to maintain the internal bonding force of the coating and prevent the coating from cracking and falling off. Adding metallic nickel to tungsten can effectively maintain the internal bonding force of the coating. At the same time, a large number of experiments have confirmed that this nickel-tungsten alloy has a good adhesion to 1350 o C, the boat is normal within 24 hours without deformation. The use of metal nickel greatly reduces the material cost and increases the internal bonding strength of the coating. In summary, the reduction boat first forms a transition gradient layer on the collective, and then forms a boron nitride coating on the gradient layer, which can achieve the effect of anti-sticking and anti-diffusion, reduce production costs, and the reduction boat has stable performance and long service life. In order to solve the above technical problems, the technical solution of this application is as follows: A CVD preparation method for a multilayer reduction boat comprises the following steps: (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.15-0.25M, 0.4-0.5M, 0.25-0.35M and 0.1-0.2M, and the pH value of the solution is controlled between 4.3-4.5; (3) pouring the electroplating solution into the electroplating tank, placing the cleaned silicon carbide into the electroplating tank for electrodeposition; (4) After electrodeposition, the plated parts are cleaned, dried, and sintered under inert gas protection; (5) Place the sintered SiC boat in a tube furnace and heat it to 900-1100°C under a protective atmosphere. o C, vapor deposition was performed to obtain a uniform BN coating.

[0006] Preferably, in step (3), the current density during electrodeposition is 40-50 mA / cm 2 The electrodeposition temperature is room temperature and the deposition time is 100 min.

[0007] Preferably, in step (4), the sintering temperature is 600-800 o C, treatment for 1 h.

[0008] Preferably, in step (5), the protective atmosphere in the tube furnace is BCl3, NH3 and H2, and the gas flow rates are 4-6, 8-12, 40-55 mL / min, respectively.

[0009] Preferably, in step (5), the vapor deposition temperature is controlled at 900-1100 o C, the pressure is maintained at 0.45-0.55kPa, and the temperature is kept for 3h.

[0010] The coating does not stick to the boat and prevents deformation. The principle is: this application uses silicon carbide as the substrate. Unlike metal substrates, inorganic non-metallic material silicon carbide has excellent mechanical properties at high temperatures. oC working temperature. However, the surface of silicon carbide has a strong adsorption force with metal tungsten and is easy to stick to the boat, so the surface of the silicon carbide substrate is covered with the surface of boron nitride. Boron nitride has low surface energy and weak adsorption force with many materials. Therefore, the material covered with boron nitride on the surface of silicon carbide can achieve both no deformation at high temperature and no sticking to the boat. However, boron nitride has low surface energy and weak adhesion to the silicon carbide substrate, so it is easy to fall off, so the present application designs a gradient coating, and designs a nickel-tungsten alloy coating between silicon carbide and boron nitride. This technology can ensure that the reduction boat does not deform or stick to the boat during high-temperature use, and the coating has high adhesion and does not crack. In the synthesis, adding metallic nickel to tungsten can greatly reduce the material cost and increase the internal bonding strength of the coating. DETAILED DESCRIPTION Implementation Method 1

[0011] (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.15M, 0.4M, 0.25M and 0.1M, and the pH value of the solution is controlled between 4.4-4.5; (3) Pour the electroplating solution into the electroplating tank, and place the cleaned silicon carbide into the electroplating tank for electroplating. The current density during electroplating is 40 mA / cm 2 , the electrodeposition temperature is room temperature, and the deposition time is 100 min; (4) After electrodeposition, the plated parts are cleaned, dried, and heated under inert gas for 600 o C high temperature treatment for 1h; (5) The SiC boat after high temperature treatment was placed in a tube furnace and heated to a certain temperature under a protective atmosphere. BCl3, NH3 and H2 were introduced into the tube furnace for vapor deposition. The gas flow rates were 4, 8 and 40 mL / min, respectively. The vapor deposition temperature was controlled at 900 o C, the pressure was maintained at 0.45 kPa, and the temperature was kept for 3 h to obtain a uniform BN coating. Implementation Method 2

[0012] (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.2M, 0.45M, 0.3M and 0.15M, and the pH value of the solution is controlled between 4.35-4.45; (3) Pour the electroplating solution into the electroplating tank, and place the cleaned silicon carbide into the electroplating tank for electroplating. The current density during electroplating is 50 mA / cm 2 , the electrodeposition temperature is room temperature, and the deposition time is 100 min; (4) After electrodeposition, the plated parts are cleaned, dried, and heated under inert gas at 700 o C high temperature treatment for 1h; (5) Place the SiC boat after high temperature treatment in a tube furnace, heat it to a certain temperature under a protective atmosphere, introduce BCl3, NH3 and H2 into the tube furnace at gas flow rates of 5, 10, and 50 mL / min, respectively, and perform vapor deposition. The vapor deposition temperature is controlled at 1000 o C, the pressure was maintained at 0.5 kPa, and the temperature was kept for 3 h to obtain a uniform BN coating. Implementation 3

[0013] (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.25M, 0.5M, 0.35M and 0.2M, and the pH value of the solution is controlled between 4.3-4.4; (3) Pour the electroplating solution into the electroplating tank, and place the cleaned silicon carbide into the electroplating tank for electroplating. The current density during electroplating is 50 mA / cm 2 , the electrodeposition temperature is room temperature, and the deposition time is 100 min; (4) After electrodeposition, the plated parts are cleaned, dried, and heated under inert gas for 800 o C high temperature treatment for 1h; (5) The SiC boat after high temperature treatment was placed in a tube furnace and heated to a certain temperature under a protective atmosphere. BCl3, NH3 and H2 were introduced into the tube furnace for vapor deposition. The gas flow rates were 6, 12 and 55 mL / min, respectively. The vapor deposition temperature was controlled at 1100 oC, the pressure was maintained at 0.55 kPa, and the temperature was kept for 3 h to obtain a uniform BN coating. Implementation 4

[0014] (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.25M, 0.5M, 0.35M and 0.2M, and the pH value of the solution is controlled between 4.3-4.4; (3) Pour the electroplating solution into the electroplating tank and place the cleaned silicon carbide into the electroplating tank for electrodeposition. The current density during electrodeposition is 50 mA / cm 2 , the electrodeposition temperature is room temperature, and the deposition time is 100 min; (4) After electrodeposition, the plated parts are cleaned, dried, and heated under inert gas for 800 o C high temperature treatment for 1h; (5) The SiC boat after high temperature treatment was placed in a tube furnace and heated to a certain temperature under a protective atmosphere. BCl3, NH3 and H2 were introduced into the tube furnace for vapor deposition. The gas flow rates were 6, 12 and 40 mL / min, respectively. The vapor deposition temperature was controlled at 1000 o C, the pressure was maintained at 0.55 kPa, and the temperature was kept for 3 h to obtain a uniform BN coating. Implementation method 5

[0015] (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.25M, 0.5M, 0.35M and 0.2M, and the pH value of the solution is controlled between 4.3-4.4; (3) Pour the electroplating solution into the electroplating tank, and place the cleaned silicon carbide into the electroplating tank for electroplating. The current density during electroplating is 50 mA / cm 2 , the electrodeposition temperature is room temperature, and the deposition time is 100 min; (4) After electrodeposition, the plated parts are cleaned, dried, and heated under inert gas protection for 800 o C high temperature treatment for 1h; (5) Place the SiC boat after high temperature treatment in a tube furnace, heat it to a certain temperature under a protective atmosphere, introduce BCl3, NH3 and H2 into the tube furnace at gas flow rates of 6, 12, and 50 mL / min, respectively, and perform vapor deposition. The vapor deposition temperature is controlled at 1000 o C, the pressure was maintained at 0.55 kPa, and the temperature was kept for 3 h to obtain a uniform BN coating.

[0016] Comparative Sample 1: A silicon carbide boat without any coating sprayed thereon.

[0017] Table 1 Effect of using reduction boat

Claims

1. A CVD method for preparing a multilayer reduction boat, characterized in that: The steps include: (1) Reduction boat substrate pretreatment: The conductive silicon carbide boat substrate is ultrasonically cleaned in alcohol and acetone solutions for 20-30 minutes each, and then ultrasonically cleaned in deionized water for 20-30 minutes to clean the substrate surface; (2) Prepare the electroplating solution, dissolve nickel sulfate hexahydrate and sodium tungstate dihydrate in deionized water, add a small amount of sodium citrate as a complexing agent and pH buffer, and add a small amount of boric acid, wherein the molar concentrations of Ni ions, sodium tungstate, sodium citrate and boric acid are controlled at 0.15-0.25M, 0.4-0.5M, 0.25-0.35M and 0.1-0.2M, respectively, and the pH value of the solution is controlled between 4.3-4.5; (3) pouring the electroplating solution into the electroplating tank, placing the cleaned silicon carbide into the electroplating tank for electrodeposition; (4) After electrodeposition, the plated parts are cleaned, dried, and sintered under inert gas protection; (5) Place the sintered SiC boat in a tube furnace and heat it to 900-1100°C under a protective atmosphere. o C, vapor deposition was performed to obtain a uniform BN coating.

2. The CVD method for preparing a multi-layer reduction boat according to claim 1, characterized in that: In the step (3), the current density during electrodeposition is 40-50 mA / cm 2 The electrodeposition temperature is room temperature and the deposition time is 100 min.

3. The CVD method for preparing a multi-layer reduction boat according to claim 1, characterized in that: In the step (4), the sintering temperature is 600-800 o C, treatment for 1 h.

4. The CVD method for preparing a multi-layer reduction boat according to claim 1, characterized in that: In the step (5), the protective atmosphere in the tubular furnace is BCl3, NH3 and H2, and the gas flow rates are 4-6, 8-12, and 40-55 mL / min, respectively.

5. The CVD method for preparing a multi-layer reduction boat according to claim 1, characterized in that: In the step (5), the vapor deposition temperature is controlled at 900-1100 o C, the pressure is maintained at 0.45-0.55kPa, and the temperature is kept for 3h.

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